[mutter] window-actor/wayland: Cleaner subsurface reordering

[Marge Bot <marge-bot src gnome org>]

commit f7768874e5ec2a808ccec424ed9e238e3dc13987
Author: Robert Mader <robert mader posteo de>
Date:   Fri Apr 16 15:15:41 2021 +0200

    window-actor/wayland: Cleaner subsurface reordering
    
    Currently when reordering subsurfaces, we un- and reparent all child
    actors of the window actor. This is unnecessarily wasteful and
    triggers bugs in clutter. While the underlying issue should be fixed
    eventually, simply reorder the actors with the tools clutter provides
    us with, avoiding those bugs and likely being faster as well.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1831>

 src/compositor/meta-window-actor-wayland.c | 65 ++++++++++++++----------------
 1 file changed, 31 insertions(+), 34 deletions(-)
---
diff --git a/src/compositor/meta-window-actor-wayland.c b/src/compositor/meta-window-actor-wayland.c
index 7c3be56904..b1fe616415 100644
--- a/src/compositor/meta-window-actor-wayland.c
+++ b/src/compositor/meta-window-actor-wayland.c
@@ -32,37 +32,36 @@ struct _MetaWindowActorWayland
 
 G_DEFINE_TYPE (MetaWindowActorWayland, meta_window_actor_wayland, META_TYPE_WINDOW_ACTOR)
 
-static gboolean
-remove_surface_actor_from_children (GNode    *node,
-                                    gpointer  data)
+typedef struct _SurfaceTreeTraverseData
 {
-  MetaWaylandSurface *surface = node->data;
-  MetaSurfaceActor *surface_actor = meta_wayland_surface_get_actor (surface);
-  MetaWindowActor *window_actor = data;
-  ClutterActor *parent;
-
-  parent = clutter_actor_get_parent (CLUTTER_ACTOR (surface_actor));
-  if (!parent)
-    return FALSE;
-
-  g_return_val_if_fail (parent == CLUTTER_ACTOR (window_actor), FALSE);
-
-  clutter_actor_remove_child (CLUTTER_ACTOR (window_actor),
-                              CLUTTER_ACTOR (surface_actor));
-
-  return FALSE;
-}
+  MetaWindowActor *window_actor;
+  int index;
+} SurfaceTreeTraverseData;
 
 static gboolean
-add_surface_actor_to_children (GNode    *node,
-                               gpointer  data)
+set_surface_actor_index (GNode    *node,
+                         gpointer  data)
 {
   MetaWaylandSurface *surface = node->data;
   MetaSurfaceActor *surface_actor = meta_wayland_surface_get_actor (surface);
-  MetaWindowActor *window_actor = data;
-
-  clutter_actor_add_child (CLUTTER_ACTOR (window_actor),
-                           CLUTTER_ACTOR (surface_actor));
+  SurfaceTreeTraverseData *traverse_data = data;
+
+  if (clutter_actor_contains (CLUTTER_ACTOR (traverse_data->window_actor),
+                              CLUTTER_ACTOR (surface_actor)))
+    {
+      clutter_actor_set_child_at_index (
+        CLUTTER_ACTOR (traverse_data->window_actor),
+        CLUTTER_ACTOR (surface_actor),
+        traverse_data->index);
+    }
+  else
+    {
+      clutter_actor_insert_child_at_index (
+        CLUTTER_ACTOR (traverse_data->window_actor),
+        CLUTTER_ACTOR (surface_actor),
+        traverse_data->index);
+    }
+  traverse_data->index++;
 
   return FALSE;
 }
@@ -75,20 +74,18 @@ meta_window_actor_wayland_rebuild_surface_tree (MetaWindowActor *actor)
   MetaWaylandSurface *surface = meta_surface_actor_wayland_get_surface (
     META_SURFACE_ACTOR_WAYLAND (surface_actor));
   GNode *root_node = surface->subsurface_branch_node;
+  SurfaceTreeTraverseData traverse_data;
 
+  traverse_data = (SurfaceTreeTraverseData) {
+    .window_actor = actor,
+    .index = 0,
+  };
   g_node_traverse (root_node,
                    G_IN_ORDER,
                    G_TRAVERSE_LEAVES,
                    -1,
-                   remove_surface_actor_from_children,
-                   actor);
-
-  g_node_traverse (root_node,
-                   G_IN_ORDER,
-                   G_TRAVERSE_LEAVES,
-                   -1,
-                   add_surface_actor_to_children,
-                   actor);
+                   set_surface_actor_index,
+                   &traverse_data);
 }
 
 static void